ASTEROIDEA 53 



jilates. It is also regarded as representing a separate subfamily, 

 Ctenodiscince. It may, however, suffice here just to mention these 

 facts, otherwise leaving the genus in the family Porcellanasteridse 

 to which it has usually been referred and to which it is, at any 

 rate, closely related. 



1. Ctenodiscus Miiller and Troschel. 



General form stellate. Aboral side covered with paxillse. Both 

 upper and lower marginal j^lates naked, but each with a single, 

 conical, rather strong spine near the upper margin. Cribriform 

 organs between all the marginal plates, but covered by a web of 

 papillae along the edge of the plates ; they continue as simple 

 channels, covered by similar webs, over the oral interradial area 

 and between the adambulacral plates. No anal opening. 



Only one species in the British seas, and, indeed, in all 

 northern seas. 



1. Ctenodiscus crispatus (Retzius). (Fig. 30.) 

 (Syn. Ctenodiscus corniculatus (Linck).) 

 Disk flat, underside somewhat convex. Arms o (exception- 

 ally 6 or 4), varying very considerably in length; R= 1-6-3 r. 



Fig. 30. — Ctenodiscus rrisjxttu-s. From tlie oral and dorsal side. Nat. size. 



Marginal, oral interradial and adambulacral plates covered by 

 a thin, soft skin. Adambulacral plates with 3-5 short, skin- 

 covered spines, the two middle ones the larger. Ambulacral 



